Genetic Influences on the Overlap Between Low IQ and Antisocial Behavior in Young Children

The well-documented relation between the phenotypes of low IQ and childhood antisocial behavior could be explained by either common genetic influences or environmental influences. These competing explanations were examined through use of the Environmental Risk Longitudinal Twin Study 1994–1995 cohort (Moffitt & the E-Risk Study Team, 2002) of 1,116 twin pairs and their families. Children’s IQ was assessed via individual testing at age 5 years. Mothers and teachers reported on children’s antisocial behavior at ages 5 and 7 years. Low IQ was related to antisocial behavior at age 5 years and predicted relatively higher antisocial behavior scores at age 7 years when antisocial behavior at age 5 years was controlled. This association was significantly stronger among boys than among girls. Genetic influences common to both phenotypes explained 100% of the low IQ–antisocial behavior relation in boys. Findings suggest that specific candidate genes and neurobiological processes should be tested in relation to both phenotypes.

Remembering the outrage the last time I posted material of this nature, I shall stick to snipping the more interesting bits of text out and not add my own comments.

The exclusion of children who received a diagnosis of ADHD had no effect on our findings regarding the gender difference in the strength of the association between low IQ and antisocial behavior.

Furthermore, it is important to note that once children with ADHD diagnoses were excluded from the sample, the low IQ–antisocial behavior correlation in girls was attenuated to almost nonsignificance. These findings suggest that the low IQ–antisocial behavior relation in girls is largely an artifact of comorbid ADHD.

The population prevalence of early-onset antisocial behavior that is life-course persistent is low (5% among men, less than 1% among women); however, these individuals account for more than their share of crime (Robins, 1966). Low IQ predicts the chronicity of antisocial behavior (Lahey et al., 1995); therefore, the children in our study who are boys, have low IQs, and have high levels of early antisocial behavior are at high risk for becoming life-course persistent antisocial individuals. This antisocial subtype is at the highest risk for myriad negative outcomes in adulthood, including mental health problems, substance dependence, financial problems, drug-related violent crime, and violence against women and children (Moffitt, Caspi, Harrington, & Milne, 2002). Genetic influences on IQ and antisocial behavior suggest that the parents of these vulnerable children are also likely to have low IQ and to be antisocial. Such parents are at risk for creating family environments that aggravate rather than ameliorate their children’s vulnerabilities. Thus, the families of young boys with low IQ who exhibit high levels of antisocial behavior should be targeted for early intervention.

One of the pieces of info I picked up from this was that … The prevalence of this research diagnosis of ADHD was 8% (70% boys; 30% girls). Also that the genders scored the same for IQ. I can’t help wondering if the abscence of these lower IQ antisocial boys from school during their teen years might not be part of the reason for the occasional finds of slightly higher IQ’s in the boys- the misssing lower IQ males boost the male average (tucked away in specialist schools, or just absent due to truancy or abandoning school at an early age.

“The population prevalence of early-onset antisocial behavior that is life-course persistent is low (5% among men, less than 1% among women); however, these individuals account for more than their share of crime (Robins, 1966). ”

But if life-course persistent anti-social behavior is so low, how can it be so heavily linked to IQ?